by RHKTriton on Sat Dec 02, 2017 11:27 am
O'guy; assuming you're talking AC fan, you'd have to find the trigger wire from the ecu to the ac fan relay. This probably gets pulled to ground by the ecu to activate (you'd have to confirm wiring diagram and/or meter). You could install a switch that performs the same task in parallel, that also grounds the negative end of a LED indicator. You would have to have some knowledge of electrics pursuing this method or you could damage the ecu.
Alternatively, I'd suggest sussing out the polarities that appear on the actual fan wires and simply install another relay and switch to drive the fan. This provides an independant backup to drive the fan and keeps you away from any ecu wiring.
On my electric radiator fan, I put in an override switch as both backup to the thermostat and as a means of blowing some air through the engine bay after a hard slog.
Don't let the b'strds get you down!!